PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM DATA_SET_ID = "RO-C/CAL-ALICE-2-ESC1-V2.0" PRODUCT_CREATION_TIME = 2010-03-26T19:10:00 PRODUCT_ID = "ALICE_DATA_TO_RAYLEIGHS" OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2010-04-01 NOTE = "Description of the how to convert calibrated Alice data (CODMAC level 3 or 4) data from the default flux units to units of Rayleighs per Angstrom." END_OBJECT = TEXT END The primary data extension of CODMAC level 3 Rosetta Alice data (SCI) is in flux units (photons cm^-2 s^-1). To convert to differential flux units, it is neccesary to first divide the image by the dispersion for each pixel. This is approximately 1.73 Angstroms/pixel, however it varies across the detector. The following IDL code illustrates how this could be done: IDL> rdfits_struct, SCI_filename, data IDL> dlambda = data.im2 - shift(data.im2, -1) IDL> dlambda[1023,*] = dlambda[1022, *] IDL> data.im0 /= dlambda In the above example, data.im0 will now be in units of photons cm^-2 s^-1 Angstrom^-1. Linearized Alice data (LIN) are already in these units. To convert from photons cm^-2 s^-1 Angstrom^-1 to Rayleighs per Angstrom (10^6 / (4 Pi) photons cm^-2 s^-1 sr^-1 A^-1) it is necessary to multiply each pixel by 4 Pi/10^6. Finally the pixels in each row of the detector must be divided by the solid angle subtended by the source. In the case of a uniformly illuminated slit, this solid angle is that subtended by that detector row. Rows subtend approximately 0.30 degrees in the spatial direction and between 0.05 and 0.10 degrees in the spectra dimension. The following list gives the solid angle (in units of steradians) subtended by each row as a function of row number (zero-indexed): Row Number Solid Angle 0 NaN 1 NaN 2 NaN 3 NaN 4 NaN 5 9.38222e-06 6 9.38222e-06 7 9.38222e-06 8 9.38222e-06 9 9.38222e-06 10 9.38222e-06 11 9.38222e-06 12 7.03666e-06 13 4.69111e-06 14 4.69111e-06 15 4.69111e-06 16 4.69111e-06 17 4.69111e-06 18 4.69111e-06 19 9.38222e-06 20 9.38222e-06 21 9.38222e-06 22 9.38222e-06 23 9.38222e-06 24 NaN 25 NaN 26 NaN 27 NaN 28 NaN 29 NaN 30 NaN 31 NaN